In many instances the current technology for automatic sharpening of knife blades depends upon sharpening of the blade by flexible emery bands which traverse the reciprocating blade while the knife is in operation. While the machine is running and the knife blade reciprocating, the operator activates a reversing lead screw causing the sharpening unit down the full length of the reciprocating blade and back up to the stop position During this traverse a drive train rotates two flexible emery bands set at some angle to the blade. The bevel on the knife edge is controlled and maintained by spring loading of the bands against the blade.
There are a number of limitations of the current method of automatic sharpening of knife blades. These are as follows; the flexible emery bands do not maintain an accurate and reproducible contact angle with the reciprocating blade. The rotating emery bands actually grind material away from the blade thus causing the bevel edge material to move towards the edge creating a burred edge. The constant reciprocation of the blade tends to remove the excessive side material and straigten the edge to some extent. The actual cutting edge is being formed by material which has yielded off the beveled face which has been cold worked and no longer has the structural integrity of the base blade. In a number of cases sections of the sharpened edge can break off in the form of a very thin wire. It is extremely difficult to sharpen a harder and more brittle alloy blade using the current method.
It is well known that control of the bevel angle is critical to the application of a knife edge. A utility knife comes in contact with the various materials of different hardness so the edge must be able to resist bending, chipping and flaking. Therefore the blade is sharpened to an angle which cuts yet remains relatively sharp under adverse conditions. This basic angle is 20.degree. to 25.degree. as measured from the centerline of the blade. By contrast, a razor is designed to cut softer material and is not subjected to impact. Therefore a razor can be sharpened to a more acute angle of 7.degree. to 10.degree. as measured from the centerline of the blade.